This ticket was mentioned in IRC in #wordpress-dev by johnbill_. ​View the logs.

Unlike the other oEmbed providers that we've added for 4.0, I'm not so convinced about Wistia's establishment or popularity. While its WordPress plugin has a reasonable number of downloads, the other numbers (Twitter followers, general Google search results, etc) aren't so great. Not a lot of people seem to be talking about Wistia.

In addition, if Wistia supports oEmbed discovery and uses an iframe for its oEmbeds, it will be supported via the oEmbed discovery which was enabled along with WordPress embeds in 4.4 and thus negates the requirement to be whitelisted.

It's neat that there's still interest here, and I think Wistia is a great platform, but with their official plugin, updated API, and support for oEmbed out of the gate, I don't see any reason to add Wistia to the providers list in core anymore.